digraph g
{

  /* list of nodes */
  "a";
  "b";
  "c";
  "d";
  "e";

  /* list of edges */
  "a" -> "b";
  "a" -> "c";
  "b" -> "c";
  "b" -> "d";
  "c" -> "d";
  "c" -> "e";
  "e" -> "e";
}